Organometallics 1993,12, 529-534
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Ring Insertion Reactions of Silaaziridines with Aldehydes and Isocyanates A. G. Brook,* Davood Azarian,+Alfred Baumegger, S. S. Hu, and Alan J. Lough Lash Miller Chemical Laboratories, University of Toronto, Toronto M5S 1A l , Ontario, Canada Received September 16,1992 Silaaziridines 5, derived from the reactions of silenes with isonitriles, react at room temperature in the dark with aromatic and a,&unsaturated aldehydes to give 1-sila-2-oxacyclopentan-5imines 7 and with aromatic isocyanates under photolytic conditions to give substituted 5-methylene-l-sila-2,4-diaza-3-oxocyclopentanes 10. These new five-membered ring heterocycles have been characterized by ‘H, I3C, and ?3i NMR spectroscopy and by the crystal structures of three compounds. Mechanisms are proposed to account for the formation of the products. We have recently reported that silenes of the family (MesSi)zSi=C(OSiMe3)R(2) react with isonitriles to yield silaaziridines 5l and not the anticipated silacyclopropanimines 3 (Scheme I). Some evidence was found which suggested that the silacyclopropanimines 3 were unstable intermediates formed in the course of the reaction, and it is significant that a disilacyclopropanimine has been reported as the product obtained from the reaction of a disilene with an isonitrile.2 The failure to observe cyclopropanimines 3 as stable products of the reactions suggested that one of the siliconcarbon ring bonds in 3 was easily broken, possibly facilitated by solvent (or some reagent) RS forming a pentacoordinated silicon species which then ring-opened, yielding the charge-delocalized hybrid 4 4’. This species appeared to be a possible intermediate in the conversion of 3 to 5 as shown in Scheme I. It was also shown that aryl isonitriles inserted into the ring Si-N bond of silaaziridines, yielding substituted 1-sila-3-azacyclobutanes6.3 This result suggested that the species 4 4‘ could also arise from the ring opening of the silaaziridines 5, followed by insertion of the aryl isonitrile to give 6. Thus it was of interest to see if the postulated intermediate 4 4’ could be trapped from reactions of silaaziridines with other reagents. When the silaaziridines 5 were treated with aromatic or a,fl-unsaturated aldehydes in the dark at room temperature for 1-3 days the heterocycles 7RR’ were formed in good yield (see Scheme 11). There was no evidence for the formation of the isomeric heterocycles 8, although the presence of trace amounts of 8 in the crude reaction mixture cannot be excluded. No reaction occurred in the dark when acetaldehyde or propionaldehydewere used or when ketones such as acetone, methyl vinyl ketone, or benzophenone were employed. However, if the solution containing the silaaziridine and acetaldehyde was photolyzed at 3360 nm, reaction slowly occurred to give the corresponding insertion compound. It follows from these observations that the silaaziridines must be able to revert back to their precursor intermediates
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+ On leave from the Department of Chemistry, Bu-Ali Sine University, Hamadan, Iran. (1) Brook, A. G.; Kong, Y. K.; Saxena, A. K.; Sawyer, J. F. Organometallics 1988, 7, 2245. ( 2 ) Yokeleon, H. B.; Millevolte, A. J.; Haller, K. J.; WBst, R. J . Chem. SOC.Chem. Commun. 1987, 1605. (3) Brook, A. G.;Saxena, A. K.; Sawyer, J. F. Organometallics 1989,
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4 4‘ under mild conditions, possibly through a fivecoordinated silicon species arising from interaction of the ring silicon atom with the oxygen atom of the carbonyl group. Contributor 4, formed from reaction of the silaaziridine with an aldehyde, as shown in Scheme 11, must then undergo ring closure to the observed adduct 7RR’ as a result of attack by the negatively chargedcarbon atom of 4 on the positively charged carbon of the aldehyde. The fact that only aryl aldehydes undergo this reaction in the dark suggests that resonance stabilization of the carbocationic center of the intermediate 4 by the arylgroup is essential for the reaction to proceed at a reasonable rate. That the reaction with acetaldehyde only occurred when the reaction mixture was photolyzed at wavelengths where the silaaziridine is known to absorb suggests that a different mechanism is probably involved. When the silaaziridines were treated with aromatic isocyanates (R”= Ph, p-Tol) no reaction occurred in the dark, but when the solution of silaaziridine and isocyanate was photolyzed at 3360 nm the heterocycles LORR” were formed as shown in Scheme 111. No reaction was observed when tert-butyl isocyanate was employed. The role of the radiation is not presently understood but presumably facilitates opening the silaaziridine ring, thus allowing the formation of the intermediate 9’, the isocyanate analog of 4’ as shown in Scheme 111. Ring closure to LORR” then occurs by attack of the charged nitrogen atom in 9‘ on the carbonyl carbon atom of the isocyanate moiety. In this case there was no evidence for the formation of 11 in the reactions, which would be derived from the participation of contributor 9 in product formation, It is of interest that different contributors to 4 4’ (or 9 9’) are trapped apparently exclusively by the two different reagents. Most reactions proceeded in high yield, as indicated by the NMR spectra of the crude reaction mixtures, which showed the absence of more than trace amounts of other products. In a few cases small amounts ( 3u(I)] 0.0006 0.0004 0.0004 weighting g 0.046 0.050 0.040 R 0.049 0.053 0.047 R W 1.18 1.41 1.39 goodness of fit 0.0 15 0.002 0.001 largest A/u 308 37 1 352 no. of params refined 0.24 0.28 0.25 max density in A F map, e/A3 = 17.2 Hz (trans)),6.51 (lH, HD,d X d X d). 13C NMR: 6 0.70, 0.76 (Measi),4.27 (OSiMe3),29.53 (AdCH),30.27 (MeC-N),37.64, 38.42 (Ad CH2),42.85 (Ad quat C), 59.94 (MesC-N),84.47 (ring CH), 87.74 (ring C-OSiMe3), 112.31 ( C H p ) , 138.11 (=CH-), 184.95 (C=N). 29SiNMR 6 4.64 (OSiMe3),-4.54 (ringSi),-13.99, -14.64 (Me3Si). Reaction of Silaaziridine Sa with Acetaldehyde. Formation of load. A solution of 0.025 mmol of silaaziridine 5a was prepared as above, and then 0.028 mmol of acetaldehyde was added by microsyringe in the dark. The reaction was monitored by 1H NMR spectroscopy, and no reaction occurred over 2 days. The reaction mixture was then photolyzed over 4 days at room temperature by which time most of the reagents had been converted to load. Removal of the solvents gave a viscous oil which failed to crystallize. 1H N M R 6 0.30,0.31,0.33 (each 9H, s, Measi), 1.19 (>9H, s, t-Bu), 1.20 (d partly overlapped with t-Bu, Me), 1.6-2.0 ( E H , m, Ad), 5.22 (lH, q, ring CH, J = 5.8 Hz). NMR 6 0.31, 1.13 (MesSi), 2.02 (OSiMes), 26.23 (MeCHI, 28.60, 28.92 (Ad CH and Me&), 36.85, 40.44 (Ad CH2), 39.96 (Ad quat C), 59.50 (Me3C),86.89 (ring CH), 119.89 (ring quat CO), 188.22 (C=N). 29Si N M R 6 12.54 (OSiMea), -5.68 (ring Si), -16.14, -16.78 (Me&. Reaction of Silaaziridine 5a with Phenyl Isocyanate. Formation of 10aa. A solution of 0.25 mmol of acylsilane la and 0.25 mmol t-BuN=C: in 0.6 mL of C6D6 was photolyzed for 2 days. NMR spectroscopy indicated that all the acylsilane had been converted to silaaziridine 5a. To this solution was added 0.25 mmol of phenyl isocyanate by microsyringe, and the solution was photolyzed for about 24 h, at which time all reagents had been converted into product 10aa. The reaction mixture was concentrated under reduced pressure, and the residue was chromatographed on silica gel using hexanes/ether (7030) followed by recrystallization from hexanes to yield colorless adduct; mp 170-173 OC. Anal. Calcd for C ~ Z H M N Z OC, ~ 62.74; S~: H, 9.19; N, 4.57. Found: C, 62.59; H, 9.40; N, 4.56. MS: calcd 612.34189, found 612.33830. 1H NMR: 6 -0.04,0.32,0.39 (each 9H, s Me&), 1.68 (9H, s, t-Bu), 1.6-1.95 (15H, m, Ad), 6.5-7.4 (5H, m, Ph). NMR 6 0.44, 1.29 (Me&), 2.34 (OSiMes), 28.41,29.76 (Ad CH andMe3C),36.56,40.66 (Ad CH2),40.04 (Ad quat C),61.03 (Me&-N), 115.58 (ring C=), 125.28,128.44,128.82 (Ph CH), 142.77 (Ph ipso C), 160.43,163.63 (C=C, C=O). 29Si NMR 6 16.30 (OSiMes), -8.65 (ring Si), -14.12, -18.20 (MesSi). IR (KBr): 1679 cm-l (C=O). MS (m/e (%)): 612 (18,M+),556 (24, M+- C4Hs),540 (59, M+ + H - Me&), 483 (41,556 - Me&), 468 (45), 467 (70), 73 (100, Me&+).
Reaction of Silaaziridine 5b with Phenyl Isocyanate. Formation of 10ba. Asolution of 0.4 g (1.20 mmol) of acylsilane lb and 0.105 g of tert-butyl isocyanide in 4 mL of C6D6 was photolyzed for 2 days, during which time the acylsilane was converted to silaaziridine 5b as shown by NMR spectroscopy. The resulting yellow solution was then concentrated under reduced pressure to remove the residual isonitrile. The residue was redissolved in 4 mL of C&, 0.15 g (2.42 mmol) of phenyl isocyanate was added, and the reaction was left for 24 h, by which time no reaction had occurred. The solution was then photolyzed for 3 days, by which time the silaaziridine had been converted to adduct lOba essentially quantitatively. The yellow oily residue remaining after removal of the solvent under reduced pressure was recrystallized from hexane at about -20 "C to produce colorless crystals: mp 126-128 "C. Anal. Calcd for CzeH~02N2Si4: C, 58.43; H, 9.36; N, 5.24. Found C, 58.07; H, 9.20, N, 5.29. MS: calcd for M+ 534.2949, found 534.2956. IH N M R 6 -0.02, 0.28, 0.35 (each 9H, s, Me&), 1.14, (9H, s, MesC-C), 1.64 (9H, s, Me3C-N),6.93-7.26 (5H, m, Ph). 13CNMR: 6 0.67,1.39 (Me3Si),2.14 (OSiMes),29.44 (MeC-C), 29.95 (Me&-N), 37.05 (Me&C), 60.67 (Me&-N), 115.80 (ring C=), 125.31,128.50,128.73(Ph CH), 142.46 (Ph ipso C), 160.01, 163.68 (C=C, C 4 ) . 29Si N M R 6 16.06 (OSiMes), -8.86 (ring Si), -14.47, -18.41 (Me&). MS (m/e ('%)): 534 (21, M+), 519 (1, M+ - Me), 478 (26, M+ C4Hs),463 (M+ - NCMea), 405 (60), 389 (93), 73 (100, Me3SP). IR: (KBr) 1673 cm-l (C=O). Reaction of Silaaziridine 5a with pTolyl Isocyanate. Formation of 10ab. The same methodology was employed as described above for lOba (including the photolysis) except that p-tolyl isocyanate was employed. Workup gave a solid material, which was chromatographed on silica gel using hexane/ether (70 30) and then recrystallized from hexanes to give colorless crystals: mp 158-159 "C. Anal. Calcd for C33H~aN202Si4:C, 63.26; H, 9.26; N, 4.47. Found: C, 63.25; H, 9.44; N, 4.43. MS: calcd for M+ 626.35754, found 626.35522. 'HN M R 6 0.03,0.36, 0.42 (each 9H, s MesSi), 1.72 (9H, s, Me&), 1.6-2.1 (Ad), 2.06 (3H, s, Me of p-tol), 6.93 (2H, d, A part of aryl A2B2 system, J = 8.1 Hz), 7.17 (2H, d, B part). 13CNMR 6 0.51, 1.33 (Me&), 2.35 (OSiMes),20.61 (Me),29.77 (Me&-N), 28.41 (Ad CH), 36.57, 40.67 (Ad CH2),40.02 (Ad quat), 60.96 (Me&-N), 115.68 (ring C=), 128.32, 129.47 (each 2C of p-tol), 134.68, 139.99 (quat C p-tol), 160.34, 163.78 (C=C and C=O). WSi NMR 6 16.16 (OSiMes), -9.16 (ring C), -14.22, -18.33 (Me&). IR (Nujol): 1681 cm-' (C=O). MS (m/e (%)): 626 (11,M+),570 (22, M+ -
Brook et al.
534 Organometallics, Vol. 12, No.2, 1993 C4H& 555 (47), 554 (49, M+ + H - Me&, 497 (44), 481 (70), 135 (49, Ad), 73 (100, MesSi+). Reaction of Silaaziridine 5b with p T o l y l Isocyanate. Formation of 10bb. Following the preceding methodology but using p-tolyl isocyanate, reaction led to the formation of lObb in near-quantitative yield. After concentration, chromatography on silica gel using hexanes/ether (8020) followed by recrystallization from hexanes gave colorless crystals: mp 137-139 'C. Anal. Calcd for C2,H52N202Si4: Cy 59.12; H, 9.49; N, 5.11. Found C, 58.96, H, 9.71; N, 5.09. MS: calcd for M+ 548.31059, found 548.30943. 1H NMR: 6 0.04,0.32, 0.38 (each 9H, 8, Me3Si), 1.17 (9H, s,MeC-C), 1.68 (9H, s,Me3C-N),2.07 (Me ofp-tol), 6.95 (2H, d, HAof AzBz system, J = 8.1 Hz), 7.17 (2H, d, HB of A2B2. 13C NMR 60.68,1.40 (Measi), 2.11 (OSiMe3),20.61 (Me), 29.45,29.94 (Me&-C andMe3C-N),37.02 (Me3C-C),60.64 (Me&N), 115.88 (ringC=), 128.44,129.42(CH ofp-tol), 135.79,139.68 (quat C of p-tol), 159.90, 163.92 ( C = O and C=C). %i NMR 6 16.01 (OSiMea), -9.33 (ring Si), -14.53, -18.48 (Measi). IR (Nujol): 1672 cm-1 ( ( 2 4 ) . MS (mle (%)): 548 (27, M+), 492 (29, M+ - CdHs), 477 (70), 476 (69), 419 (61), 403 (100, M+ + H - 2MesSi?), 73 (92, MesSi+). Attempted Reaction of Silaaziridine 5a with tert-Butyl Isocyanate or Phenyl Isothiocyanate. When silaaziridine lOaa prepared as described above was treated with excess tertbutyl isocyanate, or phenyl isothiocyanate, no reaction occurred over 48 h in the dark, as shown by the lH NMR spectrum. Extending the time, or photolyzing the solution for 24 h, failed to effect any reaction. X-ray Structural Determinations. Compounds 7aa, 7ad, and lOba were stable to air exposure during the course of the structure determination. Intensity data for the compounds were collected on a Enraf-Nonius CAD-4 diffractometer at room temperature, using graphite-monochromated Mo K a radiation (A = 0.710 73 A). The w 2 e scan technique was applied with variable scan speeds. The intensities of three standard reflections measured every 2 h showed no decay.
The structures were solved by direct methods. C, 0, and Si atoms were refined anisotropically by full-matrix least-squares = a2(F)+ gP. Hydrogen to minimize Xw(F, - Fe)*,where atoms were positioned on geometric grounds (C-H = 0.95 A, U(H) = U(C) 0.01 Az)for 7aa and 7ab, and for lOba an overall hydrogen atom thermal parameter was refined to 0.105 (4)A2. Crystal data, data collection, and least-squares parameters are listed in Table I. All calculations were performed using SHELX769and SHELXS86,10SHELXTLPC,lland NRCVAX12 on a 486-33personal computer and an Apollo computer. OrtepI3 diagrams of the structures are given in Figures 1-3.
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Acknowledgment. This research was supported by the Natural Science and Engineering Council of Canada. D.A. is grateful to the Government of the Islamic Republic of Iran for a grant facilitating his sabbatical leave. Supplementary Material Available: Tables of atomic coordinates, complete bond lengths and angles, anisotropic thermal parameters, hydrogen atom coordinates, and leastsquares planes for 7aa, 7ab, and lOba (23 pages). Ordering information is given on any current masthead page. OM9205657 ~~~
(9) Sheldrick, G. M. SHELX76, Program for Crystal Structure Determination; Cambridge University: Cambridge, England, 1976. (lO)Sheldrick, G . M. SHELXSI, Program for Crystal Structure Determination;University of Gcttingen: Federal Republic of Germany, 1986. (11)Sheldrick, G . M. SHELXTL PC Rel. 4.2., Siemens Analytical X-Ray Instruments, Inc., Karlsruhe, Germany. (12) Larson, A. C.; Lee, F. L.; Le Page, Y.;Webster, M.; Charland, J. P.; Gabe, E. J. The NRCVAX Crystal Structure System; Chemistry Division, NRC, Ottawa, Canada K1A OR6,1990. (13)Johnson,C. K. ORTEPII;ReportORNL5138;OakRidgeNational Laboratory: Oak Ridge, TN, 1976.
